Lennox furnace E200: Hard lockout — rollout circuit open
E200 is a hard lockout because the flame rollout circuit is open, or was open. Lennox's instruction is to correct the cause of the rollout trip, not simply to replace the switch.
Applies to: Lennox gas furnaces with a seven-segment diagnostic display on the control board, such as the ML193UHEK, per installation instructions 508565-01.
What it means
Rollout switches are manual-reset thermal limits mounted at the burner opening, outside the combustion chamber. They trip when flame or hot combustion gas rolls forward out of the burner box instead of being drawn through the heat exchanger and up the flue. Lennox makes this a hard lockout rather than a soft one, meaning the furnace does not clear it on a timer and try again — it stays down until the fault is recovered. That is deliberate. The wording of the code matters too: it covers a circuit that is open now or was open previously, so a rollout that tripped and was reset by hand still leaves the record behind. Lennox's stated action is to correct the cause of the trip, or replace the switch, and then test furnace operation.
Most common causes
- A blocked or restricted flue, vent or intake, so combustion gas cannot leave.
- A cracked or blocked heat exchanger.
- A failed inducer, so flue gas is not being drawn out.
- A burner problem directing flame forward out of the burner box.
- A failed rollout switch that is open with no rollout present, which is the least likely of these.
How to diagnose it
- Do not reset and rerun to get heat. A rollout trip means combustion products went somewhere they should not.
- Note whether there is any soot, scorching or discolouration visible at the front of the burner compartment.
- Confirm there is a working carbon monoxide alarm on every level of the home, including the level the furnace is on.
- Leave the rest to a licensed technician.
How to fix it
- Licensed technician only. This is the code most directly associated with combustion products entering the living space.
- Expect the flue, heat exchanger, inducer and burners to be inspected before any switch is replaced.
- Replacing the rollout switch without finding why it tripped removes the protection and leaves the cause.
Notes
Lennox's communicating alert code 200 reports the same condition on a communicating system. On this list the E prefix and the hard lockout behaviour are the distinguishing features.
Related
- Alert code 200 — Rollout limit switch open
- Which Lennox code list applies — Lennox uses two code systems that disagree on code 250
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.